Mirrors and Curved Screens

[Matt Olieman]

It doesn't matter what distance the monitor/screen is to overcome the crab effect. The only way to overcome crab effect is to center the monitor/scree from the POV.

Example: If the pilot is on the centerline of the runway, runway line infinity would be in the center of the screen. No matter what distance or how large the screen may be and the center line starts in the middle of the cockpit, the runway line infinity would be aligned to the center of the cockpit. If traveling to the runway line infinity, you would have to crab the airplane.

Collimating mirrors overcome that problem for what ever position you sit in the cockpit, the centerline of the runway always is the center of your POV.

I hope I made sense.... If not, someone please help make some sense of what I'm trying to say. Mike Powell you know what I'm talking about

Matt Olieman

[Sean Nixon]

What you say makes sense, and I remember being a little concerned about the dreaded crab effect before I started building. But I've yet to see a setup where the effect is noticeable to the extent it's off-putting. When sitting in front of a large projector screen about 6ft away from the eyepoint, I would say the view is almost identical (without close scrutiny) from either position, left hand seat or right hand seat.

[Matt Olieman]

What you say makes sense, and I remember being a little concerned about the dreaded crab effect before I started building. But I've yet to see a setup where the effect is noticeable to the extent it's off-putting. When sitting in front of a large projector screen about 6ft away from the eyepoint, I would say the view is almost identical (without close scrutiny) from either position, left hand seat or right hand seat.

Exactly Sean. I ended up moving my projector so that the center of the screen was aligned to what ever seat I was flying. Unfortunately the opposite seat would view an approach as crabbing.

Matt Olieman

[Sean Nixon]

But why would you offset the projector when the view looks acceptable from either seat when it's centered?

[Matt Olieman]

But why would you offset the projector when the view looks acceptable from either seat when it's centered?

Sorry Sean, I misread your reply.... OOPS... I thought you meant you hardly noticed the difference from closer screens......

My screen was curved, 7' wide and 10' from the pilot seat. I distinctly noticed the crab.

I got the idea of moving projectors from someone else. He made a moving (turning) projector platform for the same reason as I moved my projector. I can't recall who it was, but he did leave images here of his project (somewhere).

I guess it's all about how tolerable someone is regarding to the crabbing issue.....

Matt Olieman

[Neil Hewitt]

This is what is worrying me about my build. Because I only have about half a metre between the front windows and the wall, I can't do a front-projection and get any form of wrap-around or side-view (I only have centimeters spare between the side window and one wall of the sim room). I could mount the projector right on top of the shell at the very rear and front-project an image perhaps 2.5m wide, but it wouldn't be hugely immersive. I don't have room for a 3-screen, 3-projector set up.

My plan is to rear-project onto a screen very close to the windows, using mirrors to fold the beam and gain the necessary throw length to get a 2.5m-wide image from in front, with a curved screen that will provide a degree of wraparound and immersion, and then perhaps TFT panels on the side windows. But with the screen so close to the viewing position, the dreaded parallax problem will rear it's head. Granted, I'll be flying on my own most of the time so posititioning the center line somewhere to the left will probably help, but I'm a perfectionist, dammit

I've looked at a mirror-based solution - project onto a screen and reflect the screen in a mirror - since in theory this can be used to make the screen seem further away, but of course the image in the mirror will only be as large as the screen itself unless you can curve the mirror to create a magnifying effect, and you have to be able to curve it in both X and Y dimensions to achieve such an effect correctly. Achieving such a curve with simple acrylic mirror is beyond the capabilities of most amateurs. I guess you could heat-shape acrylic mirror onto an appropriately-shaped mould, but a) you've have to be very precise indeed, and b) I don't know what the application of heat would do to the mirror coating - it would proably stretch and break, I imagine, since it's not actually part of the acrylic itself. A mylar film mirror tensioned with a partial vacuum is what you'd need, but then that would be equivalent to a proper industrial collimating mirror and if you have the ability to produce such a thing, you're already there.

Nowhere that I could find online will sell you a pre-made spherical-section concave mirror large enough that you could use it to cover the display for a single front window in a normally-sized cockpit (say, at least 800mm across) and give you a home-made WAC (wide-angle collimated) unit. If you could get an optics or plastics outfit to make it for you, you'd have a shot, though ordering 3 or 4 isn't likely to be a large enough job for most places to be bothered.

Oh well. I'm going to make do with what I have and see how it turns out.

[mikesblack]

Thanks lineman55-

[N242AM]

Has anyone try one of the T.O.O.B setups yet?


http://www.thinkoutofbox.com/usa/

[Neil Hewitt]

It looks very cool for gaming, but because of the mirror position the seating / viewing position has to be outside the dome itself. I don't see that it's much more immersive than a single big screen in front of you in flight sim terms. What most people would like to approach must be something like Ivar Hestnes' 225-degree wraparound view. I suppose the mirror + dome arrangement goes some way towards correcting the parallax problem, depending on exactly how they've sized and placed the mirror, but the light will still be divergent and apparently focused at a point not so far ahead of you.

I could imagine you could use the same technique - project through a small hole in the screen onto a mirror and then reflect back - with a simpler curved screen and mirror sheet curved in a single axis, set at an angle towards the viewer. That might be worth researching for my own setup, actually. Thanks!

[Ferrino]

Thanks for all the replies!

I was particularly interested to learn that increased throw can alleviate some of the "defocusing" that occurs when you project onto a curved screen (i.e. "blurry side views").

One of the main uses of the curved screen I am implementing is actually driving simulations, where the lateral views are typically seen in your periphery and you don't focus on them directly (except when looking into apexes etc). So I guess the focusing problem is less severe than in flight sims, where you will spend more time looking directly at the sides than in driving sims...